(1) Field of the Invention
The present invention relates to a fiber laser system and a method for fabricating an operating element of the fiber laser system, in particular, to a passively Q-switched fiber laser system applying a novel saturable absorber as the operating element, and a method for fabricating the novel saturable absorber.
(2) Description of the Prior Art
Fiber laser has brought about many breakthroughs and progresses into the field of laser application, has replaced gas laser and traditional solid laser gradually and has become a tendency in the field of laser currently. Compared with traditional solid laser, fiber laser has such advantages as low laser threshold, high energy conversion efficiency, high beam quality, long service life, high stability etc., wherein the passively Q-switched fiber laser system is relative simple and more cost-effective.
The three main parts needed for constituting a fiber laser system are pump source, gain medium and resonance cavity. The gain medium is stimulated by the pump source to be an excited state for generating a stimulated radiation, which is amplified to form a laser after consistent oscillations inside the resonance cavity. By means of changing the design of optical devices inside the resonance cavity, two different types of laser output, continual and pulse, may be generated by the fiber laser system.
The pulsed fiber laser system may also be classified into a Q-switched laser and a mode-locked laser. The Q-switched laser generates a giant pulse with a peak power of about 100 kilowatt by compressing the pulse wand to nano-second (ns) magnitude; the mode-locked laser generates a giant pulse with a higher peak power than the Q-switched laser by compressing the pulse wand to pico-second (ps) magnitude or femto-second (fs) magnitude.
Q-switching may be classified into actively Q-switching and passively Q-switching. In actively Q-switched fiber laser systems, extensive and complex fiber pigtailed acousto-optic or electric optic devices are generally required. In such fiber laser systems, the use of high voltages and radio-frequency trigger sources makes these systems expensive and complex. Unlike actively Q-switched laser systems, passively Q-switched fiber laser systems could be made much simpler and more cost-effective by adopting saturable absorbers (SAs).
Traditional saturable absorber material includes semiconductor saturable abosorber mirrors (SESAMs), carbon nanotubes (CNTs) and graphene etc. Although SESAMs have been widely used and commercialized, their operation wavelength ranges are relatively small, they are expensive and they has a complicated processing. Although CNTs have a low saturation energy and a fast recovery, their absorbable bandwidths are relatively narrow and they are easy to be damaged. Although the graphene has a lower cost and easy fabrication, the modulation depth could be small.
If a novel saturable absorber material is developed to have properties such as large operation wavelength range, cost-effectiveness, and a low saturable absorption intensity etc., the saturable absorber material may be applied to optimize the passively Q-switched fiber laser system.